During the coming year we will pursue our recent finding that there are minor cross-reactive idiotypes, as well as the major idotype that we have been studying, associated with the anti-p-azophenylarsonate antibodies of A/J mice. These idiotypes were discovered by an analysis of the products of hybridomas. We intend to carry out a careful serological analysis of these minor idiotypes to find out how they are interrelated and in what way, if any, they are related to the major idiotype. A study of these closely related molecules should provide information relevant to the mechanism of generation of diversity of antibodies. In a collaborative project we are investigating the nature of a hapten-specific suppressor factor which can inhibit a delayed hypersensitivity reaction against the phenylarsonate group. It has already been found that this suppressor factor has antiphenylarsonate activity and that a large proportion can be bound by antibodies directed to the major idiotype. Using this system we hope to determine whether or not the suppressor factor, which is produced by a T cell, possesses determinants of light chains. We should be able to obtain a straightforward answer to this question which has been under investigation in many laboratories. We also plan to produce hybridomas which yield anti-hapten antibodies with specificities other than that directed to the phenylarsonate group. If a suitable system can be found, amino acid sequence analysis of closely related molecules will be undertaken.